Connection mechanism for automatic slack adjuster

ABSTRACT

An automatic slack adjuster for a vehicle braking system includes a yoke assembly which is pivotally mounted on the adjuster body and in which is adapted to be connected to a push rod actuated by a fluid pressure actuator. The yoke assembly includes a recess having an entrance which is adapted to receive the end of the push rod. An adapter member is threaded on the end of the push rod received in the recess, and a U-shaped connector penetrates the body of the yoke to engage a circumferentially extending groove on the adapter, to thereby define a nonthrust transmitting connection between the yoke and the push rod. The yoke assembly defines a pair of thrust receiving surfaces which circumscribe the entrance to the recess, and a thrust washer slidable on the push rod is held at a thrust transmitting engagement with one of the thrust receiving surfaces by a nut which is threaded on the end of the push rod. The adapter is stepped to define larger and smaller surfaces with a shoulder therebetween which is adapted to engage the other thrust transmitting surface. Consequently, braking thrust is exerted on the yoke assembly through the push rod, the thrust washer, and the one thrust receiving surface, but if the thrust washer is moved out of thrust-transmitting engagement with the one surface, thrust may be transmitted to the other surface through the shoulder.

This is a continuation of application Ser. No. 841,266, filed Oct. 12,1977, now abandoned.

BACKGROUND OF THE INVENTION

This invention relates to a mechanism for effecting a connection betweenthe push rod actuated by a fluid pressure actuator and a yoke assemblycarried on a slack adjuster in a vehicle fluid pressure braking system.

Modern fluid pressure braking system for heavy duty trucks include apneumatic actuator, which is communicated to an air pressure source whena brake application is effected, a push rod, which transmits movement ofthe fluid pressure actuator, and a slack adjuster, which transmitslinear motion of the push rod into rotary motion for actuating thevehicle cam actuated brakes. More recently, slack adjusters having amechanism which automatically effects brake adjustment when theclearances between the brake shoes and the brake drum become too greathave been introduced. These automatic slack adjusters include a yokeassembly which is pivotally connected to the lever which effects thebrake application and to an adjusting linkage which effects theautomatic adjustment operation. The yoke assembly is connected to thepush rod which transmits the movement of the aforementioned fluidpressure actuator. However, assembly of automatic slack adjusters to thepush rods has been quite time-consuming, particularly in view of thefact that automatic slack adjusters are commonly mounted in very tightspaces, and use push rods which are relatively short. It is thereforehighly desirable to provide a mechanism which can effect the connectionbetween the actuator push rod and the yoke assembly carried by the slackadjuster in a minimum amount of time and in a relatively simple andeffective manner.

SUMMARY OF THE INVENTION

Therefore, an important object of our invention is to provide amechanism which effects the connection between a push rod and yokeassembly of an automatic slack adjuster in a less time-consuming andmore efficient manner than those mechanisms known to the prior art.

Another important object of our invention is to provide an automaticslack adjuster which connects with the actuator push rod through amechanism having both thrust transmitting and nonthrust transmittingconnections.

Still another important object of the invention is to provide aconnection between an automatic slack adjuster and an actuator push rodwhich is fail-safe, so that braking forces can be assured of beingtransmitted to the slack adjuster when a brake application is effected.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a fragmentary plan view, partly in section, of a cam actuatedbrake having an automatic slack adjuster;

FIG. 2 is a view taken substantially along lines 2--2 of FIG. 1 andillustrating a mechanism made pursuant to the teachings of the presentinvention for connecting the slack adjuster yoke assembly and theactuator push rod, the various components being illustrated in positionswhich they assume just prior to connection of the push rod to the yokeassembly;

FIG. 3 is a view similar to that of FIG. 2 showing the variouscomponents of the connecting mechanisms in the positions which theyassume after the push rod has been secured to the yoke assembly;

FIG. 4 is a view taken substantially along lines 4--4 of FIG. 3;

FIG. 5 is a view similar to FIG. 3 but illustrating another embodimentof the invention;

FIG. 6 is a view taken substantially along lines 6--6 of FIG. 5; and

FIG. 7 is a view similar to that of FIGS. 3 and 5, but illustratingstill another embodiment of the invention.

DETAILED DESCRIPTION

Referring now to FIG. 1 of the drawings, a cam actuated brake assemblygenerally indicated by the numeral 10 includes a drum 12 which ismounted for rotation with a vehicle wheel, and a pair of brake shoes 14,16 which are yieldably urged away from the drum 12 by a return spring18. A cam 20 is mounted on a cam shaft 21 and is disposed betweencontiguous ends of the brake shoes 14 and 16. Upon rotation of the camshaft 21, the cam 20 rotates to urge the shoes 14 and 16 apart and intobraking engagement with the drum 12 in a manner well known to thoseskilled in the art. An automatic slack adjuster generally indicated bythe numeral 22 includes a lever 24 which is mounted on the cam shaft 21,and is adapted to rotate cam shaft 21 when the lever 24 is rotated. Theautomatic slack adjuster 22 further includes a yoke assembly 26 whichconnects with an actuator push rod 28 which transmits motion of a fluidpressure actuator (not shown) which is well known to those skilled inthe art and will not be described in detail herein. The lever 24transmits the linear motion of the push rod 28 into rotary motion of thecam shaft 21. The yoke assembly 26 is pivotally connected to the lever24 as at 30 and is also pivotally connected to a linkage assembly 32.The linkage assembly 32 is part of the automatic adjustment mechanismfor the slack adjuster 22, and is effective upon movement of the shoes14 and 16 in an excessive amount during the brake application to indexthe brake release position of the shoes 14, 16 so that they are closerto the drum 12, thereby maintaining the released clearance of the brakeshoes 14 and 16 with respect to the drum 12 at a substantially constantamount. The slack adjuster 22 may be of the type described in U.S. Pat.No. 3,901,357, owned by the assignee of the present invention, andincorporated herein by reference.

The push rod 28 is normally connected to the yoke assembly 26 after boththe push rod 28, the aforementioned fluid pressure actuator (not shown),and the automatic slack adjuster mechanism 22 are already mounted on thevehicle. It will readily be appreciated by those skilled in the art thatthe connection between the push rod 28 and the yoke assembly 26 cansometimes be quite difficult, particularly in installations in tightspaces where the length of the push rod 28 is relatively short.Referring now to FIGS. 2-4, the connection mechanism of the presentinvention will be described in detail. The yoke assembly 26 terminatesin an enlarged portion 34 which defines a recess 36 therewithin havingan open end 38 which is adapted to receive the push rod 28. A pair ofopenings 40, 42 penetrate the portion 34 of the yoke assembly 26, andintersect the edges of the recess 36. An adapter 44 is threadedlyconnected to the end of the push rod 28, which is provided with threadsas at 46. The adapter 44 has a circumferentially extending groove 48provided therein which intersects the openings 40 and 42 when the end ofthe push rod 28 is installed within the recess 36 as best illustrated inFIG. 3. A generally U-shaped clip generally indicated by the numeral 50defines a pair of legs 52, 54 which are adapted to be received in theopenings 40 and 42. Again, as illustrated in FIG. 3, the end of the pushrod 28 carrying the adapter 44 is installed in the opening 36, with thegroove 48 aligned with the openings 40, 42. The legs 54, 52 of the clip50 are then inserted in the openings 40, 42, so that they engage thegroove 48 and thereby provide a nonthrust transmitting connectionbetween the yoke assembly 26 and the push rod 28. The ends of the legs52, 54 are deflected outwardly as best illustrated in FIG. 4 after theclip 50 is installed on the yoke assembly 26, to prevent the clip 50from being knocked or vibrated out of position.

The yoke 26 defines a thrust receiving surface 56 which circumscribesthe entrance 38 into the recess 36. A thrust washer 58 is slidablymounted on the push rod 28, and a conventional nut 60 is threadedlyengaged with the threads 46. After the adapter 44 and clip 50 areinstalled as described hereinabove and as illustrated in FIG. 3, thethrust washer 58 is brought in engagement with the thrust receivingsurface 56, and the nut 60 tightened to hold the thrust washer 58 snuglyagainst the surface 56 and to also take up the axial clearance betweenthe legs 52, 54 of the clip 50 and the groove 48. When this axialclearance is taken up, there will still be a small clearance between theleft hand end of the adapter 44, viewing FIG. 3, and the thrust washer58.

DETAILED DESCRIPTION OF THE FIRST ALTERNATE EMBODIMENT

Referring now to the embodiment of FIGS. 5 and 6, elements substantiallythe same as those in the preferred embodiment retain the same referencecharacter, but increased by 100. Referring now to FIGS. 5 and 6, thecircumferentially extending groove 48 of the adapter in the preferredembodiment is replaced by a pair of spirally cut grooves 162, 164 andthe openings 40, 42 of the preferred embodiment are replaced with a pairof diametrically opposed projections 166, and 168. Diametrically opposedportions of the adapter 144 are provided with flats 172, 176, as bestillustrated in FIG. 6. A hex head 178 is integral with the adapter 144,and is adapted to engage the thrust receiving surface 156 of the housing134. Therefore, when the thrust or push rod 128 is to be installed onthe yoke assembly 126, the adapter 144 is installed into the recess 136with the flats 172, 176 opposite the projection 166, 168, so that theadapter 144 may be installed in the recess 136 in the positionillustrated in FIG. 5. The hex head 178 is then rotated one-quarterturn, to thereby engage the projections 166, 168 with theircorresponding spirally cut grooves 162, 164. When this is effected,shoulder 180 defined on the hex head 178 will engage the thrustreceiving surface 156 on the housing 134, to thereby define the thrusttransmitting connection between the push rod 128 and the yoke assembly126. The nut 160 is then advanced into locking position against the hexhead 178.

DETAILED DESCRIPTION OF THE SECOND ALTERNATE EMBODIMENT

Referring now to the embodiment of FIG. 7, elements substantially thesame as those in the preferred embodiment retain the same referencecharacter, but increased by 200. Referring now to FIG. 7, the connectingmechanism shown therein is identical to that of the preferredembodiment, except that the inner circumferential surface of theenlarged portion 234 of the yoke assembly 226 is stepped to definelarger and smaller diameter portions with a shoulder 282 therebetween.Shoulder 282 defines a second thrust receiving surface, which cooperateswith a thrust transmitting surface 284 on the adapter 244. The thrusttransmitting surface 284 is defined on a shoulder between larger andsmaller diameter portions 286, 288 of the adapter 244. The thrustreceiving and transmitting surfaces 282, 284 serve as a back-up for theprimary thrust transmitting mechanism defined between the thrust washer258 and the thrust receiving surface 256. Consequently, if the nut 260should be inadvertently loosened or should vibrate away from the thrustwasher 258 allowing the latter to separate from the thrust receivingsurface 256 so that braking thrust can no longer be transmittedtherebetween, thrust will be transmitted through the secondary thrusttransmitting mechanism defined between the shoulders 284 and 282,thereby preventing failure of the vehicle's brakes, since the U-clipitself cannot withstand the braking thrust transmitted to the yoke 226.

We claim:
 1. In a vehicle braking system, a brake actuating lever, ayoke pivotally connected to said lever, a thrust rod, a fluid pressureresponsive actuator connected to said thrust rod for urging the latterin a brake application effecting and brake releasing directions andmeans attaching said yoke to said thrust rod, said yoke including arecess having an entrance through which one end of said thrust rodextends, said attaching means including an adapter movable axially onsaid thrust rod and located in said recess, first connecting meanscarried by said yoke and projecting into said recess for engagement withsaid adapter to define a connection between said yoke and said adapterwhich does not transmit braking thrust, and second connecting meanscarried by said thrust rod and cooperating with said yoke to transmitbraking thrust to the lever when a brake application is effected, saidyoke defining first and second transverse thrust-receiving surfacescircumscribing said thrust rod, said second connecting means includingfirst thrust transmitting means carried by said thrust rod forengagement with the first thrust-receiving surface, and second thrusttransmitting means carried by said adapter for engagement with thesecond thrust-receiving surface.
 2. The invention of claim 1:whereinsaid first thrust transmitting means includes means movable relative tothe thrust rod but lockable in a position to engage said firstthrust-receiving surface.
 3. The invention of claim 2:wherein said meansmovable relative to the thrust rod includes a thrust washer slidable onsaid thrust rod and a nut locking said thrust washer in place.
 4. Theinvention of claim 2:wherein said recess is stepped to define larger andsmaller diameter portions with a shoulder therebetween, the secondthrust receiving surface being defined on said shoulder.
 5. Theinvention of claim 4:wherein said adapter is stepped to define largerand smaller diameter portions with a shoulder therebetween, saidshoulder on the adapter engaging said second thrust receiving surfacewhen braking thrust is transmitted thereto.
 6. The invention of claim5:wherein engagement of said first thrust transmitting means with saidfirst thrust receiving surface holds said shoulder on the adapter awayfrom said second thrust transmitting surface whereby braking thrust isnormally transmitted between said first thrust transmitting means andsaid first thrust receiving surface but is transmitted from saidshoulder on the adapter to the second thrust receiving surface when thefirst thrust transmitting means is disposed away from the first thrustreceiving surface when a brake application is effected.